Preparation method and application of a metal-bipyridine-based bifunctional catalyst

Abstract

The present invention discloses a preparation method and application of a bifunctional catalyst based on metal-bipyridine, and belongs to the field of catalyst preparation technology. The present invention coats the metal-bipyridine polymer generated by the condensation reaction onto silicon oxide loaded with ionic liquid through a surfactant micelle solution to prepare a bifunctional catalyst based on metal-bipyridine. In the catalyst, the metal-bipyridine can be fully exposed, and the ionic liquid loaded on the silicon oxide can work well together. The obtained bifunctional catalyst can catalyze the reaction of carbon dioxide and epoxy compounds to prepare cyclic carbonates under solvent-free and co-catalyst-free conditions, and the catalyst is easy to recycle, the product purification is simple, and energy consumption is saved. The present invention provides a strategy for the preparation of efficient bifunctional catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a preparation method based on metal-bipyridine bifunctionality and application thereof. Background Art

[0002] Since the Industrial Revolution, atmospheric carbon dioxide concentrations have been rising annually. On the other hand, carbon dioxide is a vital C1 resource that can be converted into high-value-added chemicals through various methods, including thermal catalysis, photocatalysis, and electrocatalysis. The reaction of CO2 with epoxides to produce cyclic carbonates offers 100% atomic utilization, meeting the requirements of green chemistry and representing an ideal method for CO2 resource utilization.

[0003] Metal-bipyridines are often used as Lewis acid sites in conjunction with nucleophiles to react CO2 with epoxides to prepare cyclic carbonates. In their article "Hierarchical mesoporous organic polymer with an intercalated metal complex for the efficient synthesis of cyclic carbonates from flue gas" (Green Chem., 2016, 18, 6493), Chen Jian et al. reacted melamine with Zn-bipyridine dialdehyde to produce a hierarchically porous Zn-bipyridine polymer, which was then applied to the cycloaddition reaction of CO2 with epoxides. However, the addition of TBAB as a cocatalyst was required, and the product purification was difficult, making it difficult to commercialize. In their article "Poly(ionic liquids)s with high density of nucleophile / electrophile for CO2 fixation to cyclic carbonates at mild conditions" (J.CO2Util‌‌., 2019, 32, 281), Xie Yaqiang et al. reported a free radical polymerization reaction between an ethylene-functionalized imidazolium ionic liquid and bipyridine to produce an ionic polymer containing bipyridine units. This was then coupled with metal coordination to produce a series of dual-functional catalysts. The metal-bipyridine sites synergistically interacted with the imidazolium ionic liquid to efficiently catalyze the CO2 cycloaddition reaction. However, the ionic polymers are highly charged and require drying under supercritical CO2 to maintain their high surface area, a complex and energy-intensive process. In their article "Flexibility matters: cooperative active sites in covalent organic framework and threaded ionic polymer" (J. Am. Chem. Soc. 2016, 138, 15790), Sun Qi et al. introduced an ionic polymer onto a covalent organic framework containing bipyridine units via free radical polymerization of a vinyl-containing quaternary phosphonium salt ionic liquid. Subsequently, through metal coordination, they obtained a bifunctional catalyst that catalyzed the carbon dioxide cycloaddition reaction at 40°C and 0.1 MPa CO2. However, the ionic liquid polymer easily clogs the pores of the covalent organic framework, hindering the exposure of the active sites and their contact with reactants, thereby limiting their catalytic activity. Summary of the Invention

[0004] The present invention aims to provide a preparation method and application of a metal-bipyridine-based catalyst. The method is simple to operate, and the prepared catalyst has high catalytic activity, is easy to recycle, and saves energy. Moreover, the method can catalyze the reaction of carbon dioxide and epoxy compounds to prepare cyclic carbonates in the absence of solvents and catalyst promoters, and has good application prospects.

[0005] To achieve the purpose of the invention, the present invention provides a method for preparing a bifunctional catalyst based on metal-bipyridine, comprising the following steps:

[0006] (1) Add fumed silica, silane coupling agent, and nitrogen-containing monomer to dry toluene, ultrasonicate for 0.5-1h, and then control the temperature at 80-120℃ under nitrogen protection for 8-24h. Filter the reaction product, wash the solid, and dry it to obtain ionic liquid-loaded silicon oxide ILs-SiO2.

[0007] (2) Dissolve hexadecyltrimethylammonium bromide and sodium lauryl sulfate in deionized water and sonicate for 0.5-1 h to obtain a micellar solution;

[0008] The 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex and the aromatic amine monomer were dissolved in a polar organic solvent, and then added to an equal volume of the micelle solution, and ultrasonicated for 0.5-1h to obtain a first solution and a second solution;

[0009] The obtained first solution and the obtained second solution were mixed, glacial acetic acid was added, stirred for 0.5-1h, and then allowed to stand at room temperature for 8-24h to obtain a third solution;

[0010] (3) Adding ionic liquid-loaded silicon oxide (ILs-SiO2) to the third solution obtained in (2), and then stirring and reacting at room temperature for 24-48 hours. After the reaction is completed, the solid is filtered and washed, and subjected to Soxhlet extraction for 12-48 hours. Finally, it is vacuum-dried at 60-120°C for 8-24 hours to obtain a metal-bipyridine-based bifunctional catalyst.

[0011] Furthermore, in the step (1), the silane coupling agent is one of 3-bromopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane or 3-iodopropyltrimethoxysilane, and the nitrogen-containing monomer is one of N-methylimidazole, triethylamine and pyridine; and 1-3 mmol of silane coupling agent and 1.5-4.5 mmol of nitrogen-containing monomer are added to every 1 g of fumed silica.

[0012] Furthermore, in the step (2), the transition metal in the 2,2'-bipyridine-5,5'-dicarbaldehyde transition metal complex is one of Cu, Zn or Co; the aromatic amine monomer is one of 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine; and the polar organic solvent is one of dimethyl sulfoxide, N'N-dimethylformamide or dioxane.

[0013] Furthermore, in the step (2), the molar concentration ratio of sodium dodecyl sulfate to hexadecyltrimethylammonium bromide is 1:30-40; the amount of 2,2'-bipyridine-5,5'-dicarboxaldehyde metal complex used in the first solution is 10-30 mmol / L; the amount of aromatic amine monomer used in the second solution is 6.7-20 mmol / L; and the volume ratio of glacial acetic acid to the third solution is 1-3:305.

[0014] Furthermore, in the step (3), the amount of the ionic liquid-loaded silicon oxide ILs-SiO2 used is 6.6-16.4 g / L of the third solution, and the solvent used for the Soxhlet extraction is one of acetone, ethanol or tetrahydrofuran.

[0015] Another object of the present invention is to provide the use of the above-mentioned metal-bipyridine-based bifunctional catalyst in the preparation of cyclic carbonates by the reaction of carbon dioxide and epoxy compounds.

[0016] The beneficial effects of the present invention compared to the prior art are as follows:

[0017] The present invention prepares silicon oxide loaded with ionic liquid through grafting reaction and quaternization reaction, prepares metal-bipyridine polymer through aldehyde-amine condensation reaction in micellar solution and coats the polymer onto silicon oxide loaded with ionic liquid, thereby preparing metal-bipyridine-based bifunctional catalyst. The catalyst does not require the use of homogeneous co-catalyst, is simple to purify, and is conducive to industrial utilization.

[0018] This method loads an ionic liquid onto silicon oxide and composites a metal-bipyridine polymer with the ionic liquid via a micellar solution to produce a bifunctional metal-bipyridine catalyst. Hexadecyltrimethylammonium bromide and sodium lauryl sulfate in the micellar solution act as templates, facilitating pore formation. After washing and removing the template, the material can be simply dried to achieve a high specific surface area. No supercritical carbon dioxide drying is required, simplifying the preparation process and saving energy.

[0019] In the present invention, the metal-bipyridine polymer is coated on the silicon oxide grafted with the ionic liquid, and the active sites are fully exposed through an in-situ composite method in the micellar solution, thereby solving the problem that the ionic liquid polymer blocks the pores, hinders the exposure of the active sites and their contact with the reactants, and limits the catalytic activity.

[0020] The metal-bipyridine-based bifunctional catalyst provided by the present invention is used to catalyze the reaction of carbon dioxide and epoxy compounds to prepare cyclic carbonates. Under solvent-free and co-catalyst-free conditions, the yield of cyclic carbonates can reach 99%. The reaction conditions are simple, costs are reduced, the catalyst is easy to recover, and the product purification is simple. Therefore, the catalyst has good application prospects in actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a transmission electron microscope photograph of Cat2 obtained in Example 2;

[0022] Figure 2 This is the infrared spectrum of Cat2 obtained in Example 2;

[0023] Figure 3 This is the isothermal adsorption-desorption curve of nitrogen at 77K for Cat2 obtained in Example 2. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and examples, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention. Example 1

[0025] (1) 1 g of fumed silica, 1 mmol of 3-chloropropyltrimethoxysilane, and 1.5 mmol of pyridine were added to 50 mL of dry toluene. After ultrasonic treatment for 0.5 h, the mixture was reacted at 80 °C for 24 h under nitrogen protection. The reaction product was filtered, the solid was washed, and dried to obtain ionic liquid-loaded silicon oxide ILs-SiO2.

[0026] (2) Dissolve 30 mmol of hexadecyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water and sonicate for 0.5 h to obtain a micellar solution;

[0027] 0.3 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde copper complex and 0.2 mmol of 1,3,5-tris(4-aminophenyl)benzene were dissolved in 0.5 mL of dimethyl sulfoxide, and then added to 30 mL of micellar solution, and ultrasonicated for 0.5 h to obtain a first solution and a second solution respectively;

[0028] The obtained first solution and the obtained second solution were mixed, 0.2 mL of glacial acetic acid was added, and the mixture was stirred for 0.5 h, and then allowed to stand at room temperature for 8 h to obtain a third solution.

[0029] (3) 0.4 g of ionic liquid-loaded silicon oxide (ILs-SiO2) was added to the third solution obtained in (2), and the mixture was stirred at room temperature for 24 h. After the reaction, the mixture was filtered and washed. The resulting solid was subjected to Soxhlet extraction with acetone for 12 h and finally dried under vacuum at 60°C for 24 h to obtain a Cu-bipyridine-based bifunctional catalyst, named Cat1. Example 2

[0030] (1) 1 g of fumed silica, 2 mmol of 3-bromopropyltrimethoxysilane, and 3 mmol of triethylamine were added to 50 mL of dry toluene. The mixture was ultrasonicated for 0.75 h and then reacted at 100 °C for 16 h under nitrogen protection. The reaction product was filtered, the solid was washed, and dried to obtain ionic liquid-loaded silicon oxide ILs-SiO2.

[0031] (2) Dissolve 32 mmol of hexadecyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water and sonicate for 0.75 h to obtain a micellar solution;

[0032] 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde zinc complex and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine were dissolved in 0.5 mL of N'N-dimethylformamide, and then added to 30 mL of micellar solution, and ultrasonicated for 0.75 h to obtain a first solution and a second solution respectively;

[0033] The obtained first solution and the obtained second solution were mixed, 0.4 mL of glacial acetic acid was added, and the mixture was stirred for 0.75 h, and then allowed to stand at room temperature for 16 h to obtain a third solution.

[0034] (3) 0.7 g of ionic liquid-loaded silicon oxide (ILs-SiO2) was added to the third solution obtained in (2), and the mixture was stirred at room temperature for 36 h. After the reaction, the mixture was filtered and washed, and the resulting solid was subjected to Soxhlet extraction with ethanol for 30 h. Finally, the solid was vacuum-dried at 90°C for 16 h to obtain a Zn-bipyridine-based bifunctional catalyst, named Cat2. Example 3

[0035] (1) 1 g of fumed silica, 3 mmol of 3-iodopropyltrimethoxysilane, and 4.5 mmol of N-methylimidazole were added to 50 mL of dry toluene. After ultrasonic treatment for 1 h, the mixture was reacted at 120 °C for 8 h under nitrogen protection. The reaction product was filtered, the solid was washed, and dried to obtain ionic liquid-loaded silicon oxide ILs-SiO2.

[0036] (2) Dissolve 40 mmol of hexadecyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water and sonicate for 1 h to obtain a micellar solution;

[0037] 0.9 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde cobalt complex and 0.6 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine were dissolved in 0.5 mL of dioxane, and then added to 30 mL of micellar solution, and ultrasonicated for 1 h to obtain a first solution and a second solution respectively;

[0038] The obtained first solution and the obtained second solution were mixed, 0.6 mL of glacial acetic acid was added, and the mixture was stirred for 1 hour, and then allowed to stand at room temperature for 24 hours to obtain a third solution.

[0039] (3) 1.0 g of ionic liquid-loaded silicon oxide (ILs-SiO2) was added to the third solution obtained in (2), and the mixture was stirred at room temperature for 48 h. After the reaction, the mixture was filtered and washed. The resulting solid was subjected to Soxhlet extraction with tetrahydrofuran for 48 h and finally dried in vacuo at 120°C for 8 h to obtain a Co-bipyridine-based bifunctional catalyst, designated Cat3. Example 4

[0040] 10 mmol of propylene oxide and 60 mg of catalyst Cat1 obtained in Example 1 were placed in a 15 mL stainless steel reactor, sealed, and filled with 2 MPa of carbon dioxide. The reaction was then transferred to a 120°C oil bath and stirred for 4 hours. After the reaction, the reactor was cooled in an ice-water bath. Unreacted carbon dioxide was then released, and the reaction liquid was transferred to a centrifuge tube containing an internal standard (biphenyl). The reaction was centrifuged, and the supernatant was analyzed by gas chromatography. The yield of propylene carbonate was 90%. Example 5

[0041] Similar to Example 4, Cat2 obtained in Example 2 was used to replace Cat1 in Example 4, and other reaction conditions and processes remained unchanged. The yield of propylene carbonate was 99%. Example 6

[0042] Similar to Example 4, Cat3 obtained in Example 3 was used to replace Cat1 in Example 4, and other reaction conditions and processes remained unchanged. The yield of propylene carbonate was 93%. Example 7

[0043] Test the universality of catalyst Cat2: Similar to Example 6, epichlorohydrin, 1,2-epoxyhexane, and styrene oxide were used as reaction substrates to replace the propylene oxide in Example 5, while other conditions remained unchanged. The conversion rates of the substrates used are shown in the table below.

[0044] Table 1. Reaction results of the cycloaddition reaction of other epoxy compounds with carbon dioxide catalyzed by Cat2 in Example 7:

[0045] Comparative Example 1

[0046] The difference from Example 2 is that no micelle solution is used. The specific experimental scheme is as follows:

[0047] (1) 1 g of fumed silica, 2 mmol of 3-bromopropyltrimethoxysilane, and 3 mmol of triethylamine were added to 50 mL of dry toluene. The mixture was ultrasonicated for 0.75 h and then reacted at 100 °C for 16 h under nitrogen protection. The reaction product was filtered, the solid was washed, and dried to obtain ionic liquid-loaded silicon oxide ILs-SiO2.

[0048] (2) 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde zinc complex and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine were dissolved in 0.5 mL of N'N-dimethylformamide, and then added to 30 mL of deionized water, respectively. Ultrasonication was performed for 0.75 h to obtain the first solution and the second solution respectively.

[0049] The obtained first solution and the obtained second solution were mixed, 0.4 mL of glacial acetic acid was added, and the mixture was stirred for 0.75 h, and then allowed to stand at room temperature for 16 h to obtain a third solution.

[0050] (3) 0.7 g of ionic liquid-loaded silicon oxide (ILs-SiO2) was added to the third solution obtained in (2), and the mixture was stirred at room temperature for 36 h. After the reaction, the mixture was filtered and washed, and the resulting solid was subjected to Soxhlet extraction with ethanol for 30 h. Finally, the solid was vacuum-dried at 90°C for 16 h to obtain a Zn-bipyridine-based bifunctional catalyst, named Cat2'. Comparative Example 2

[0051] Without compounding with ILs-SiO2, the specific experimental scheme is as follows:

[0052] (1) Dissolve 32 mmol of hexadecyltrimethylammonium bromide and 1 mmol of sodium dodecyl sulfate in 300 mL of deionized water and sonicate for 0.75 h to obtain a micellar solution;

[0053] 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde zinc complex and 0.4 mmol of 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine were dissolved in 0.5 mL of N'N-dimethylformamide, and then added to 30 mL of micellar solution, and ultrasonicated for 0.75 h to obtain a first solution and a second solution respectively;

[0054] The obtained first solution and the obtained second solution were mixed, 0.4 mL of glacial acetic acid was added, and the mixture was stirred for 0.75 h, and then allowed to stand at room temperature for 16 h to obtain a third solution.

[0055] (2) The third solution obtained in (1) was stirred and reacted at room temperature for 36 hours. After the reaction, the solution was filtered and washed. The resulting solid was subjected to Soxhlet extraction with ethanol for 30 hours and finally dried under vacuum at 90°C for 16 hours to obtain a Zn-bipyridine-based polymer catalyst, named "Cat2". Comparative Example 3

[0056] Similar to Example 4, Cat2' obtained in Comparative Example 1 was used to replace Cat1 in Example 4, and other reaction conditions and processes remained unchanged. The yield of propylene carbonate was 72%. Comparative Example 4

[0057] Similar to Example 4, Cat2" obtained in Comparative Example 2 was used to replace Cat1 in Example 4, and other reaction conditions and processes remained unchanged. The yield of propylene carbonate was 5%.

[0058] Attachment Figure 1 The TEM image of Cat1 is given, showing that it is composed of nanospheres of about 20 nm and has no impurity phase, indicating that the metal porphyrin polymer and ILs-SiO2 can be well composited.

[0059] Attachment Figure 2 The infrared spectrum of Cat2 obtained in Example 2 is given. -1 The characteristic vibration peak attributed to C=N can be observed at 1000-1200 cm, indicating that the metal complex of 2,2'-bipyridine-5,5'-dicarboxaldehyde successfully undergoes aldehyde-amine condensation reaction with aromatic amine to form a metal bipyridine polymer; -1 The absorption peak at 2924 cm can be attributed to the vibration of Si-O-Si in ILs-SiO2. -1 、1462cm -1 、1389cm -1 It can be attributed to the CH vibration of methyl and methylene groups in the ionic liquid in ILs-SiO2.

[0060] Attachment Figure 3 The nitrogen isothermal adsorption-desorption curve of Cat2 obtained in Example 2 at 77K is given. The adsorption amount in the low-pressure region increases sharply and contains a hysteresis loop, indicating that the material has a micro-mesoporous structure, with a BET specific surface area of ​​782m 2 / g, with a total pore volume of 0.9 cm 3 / g.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bifunctional catalyst based on metal-bipyridine, characterized in that: The following steps are involved: (1) Add fumed silica, silane coupling agent, and nitrogen-containing monomer to dry toluene, ultrasonicate for 0.5-1h, and then control the temperature at 80-120°C under nitrogen protection for 8-24h. Filter the reaction product, wash the solid, and dry it to obtain ionic liquid-loaded silicon oxide ILs-SiO2; (2) Dissolve hexadecyltrimethylammonium bromide and sodium lauryl sulfate in deionized water and sonicate for 0.5-1 h to obtain a micellar solution; Dissolving a 2,2'-bipyridine-5,5'-dicarboxaldehyde transition metal complex and an aromatic amine monomer in a polar organic solvent, respectively, and then adding them to an equal volume of the micelle solution, and sonicating for 0.5-1 h to obtain a first solution and a second solution, respectively; The obtained first solution and the obtained second solution are mixed, glacial acetic acid is added, stirred for 0.5-1h, and then allowed to stand at room temperature for 8-24h to obtain a third solution; (3) ionic liquid-loaded silicon oxide ILs-SiO2 is added to the third solution obtained in step (2), and then stirred at room temperature for 24-48h; after the reaction is completed, the solid is filtered and washed, and subjected to Soxhlet extraction for 12-48h, and finally vacuum dried at 60-120°C for 8-24h to obtain a metal-bipyridine-based bifunctional catalyst; In the step (1), the silane coupling agent is one of 3-bromopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane or 3-iodopropyltrimethoxysilane, and the nitrogen-containing monomer is one of N-methylimidazole, triethylamine or pyridine; 1-3 mmol of silane coupling agent and 1.5-4.5 mmol of nitrogen-containing monomer are added to every 1 g of fumed silica.

2. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (2), the molar concentration ratio of sodium dodecyl sulfate to hexadecyltrimethylammonium bromide in deionized water is 1:30-40; the transition metal in the 2,2'-bipyridine-5,5'-dicarbaldehyde transition metal complex is one of Cu, Zn or Co; the aromatic amine monomer is one of 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-tris(4'-aminophenyl)-1,3,5-triazine; and the polar organic solvent is one of dimethyl sulfoxide, N'N-dimethylformamide or dioxane.

3. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (2), the amount of 2,2'-bipyridine-5,5'-dicarbaldehyde transition metal complex used is 10-30 mmol / L of the first solution; the amount of aromatic amine monomer used is 6.6-20 mmol / L of the second solution; and the volume ratio of glacial acetic acid to the third solution is 1-3:

305.

4. The method for preparing a bifunctional catalyst based on metal-bipyridine according to claim 1, characterized in that: In the step (3), the amount of silicon oxide ILs-SiO2 loaded with ionic liquid is 6.6 g-16.4 g / L of the third solution, and the solvent used for Soxhlet extraction is one of acetone, ethanol or tetrahydrofuran.

5. An application of a metal-bipyridine-based bifunctional catalyst prepared by the preparation method according to claim 1, characterized in that: A metal-bipyridine-based bifunctional catalyst was applied to the reaction of carbon dioxide with epoxides to prepare cyclic carbonates.

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